The optical inspection is used in most of the current biochemistry measurement devices. In the optical inspection, an illuminant is used to produce the inspection light which turns into the transmitted light or the reflected light after irradiating to the test sample. The specific range (usually +/−10 nm of the specific wave length) of spectrum is extracted by the band pass filter and the optical signal of the specific range of spectrum is transformed into the electrical signal of the specific range of spectrum by the photodiode. The electrical signals of the test sample and the calibration sample obtained from the same specific range of spectrum are compared then. According to the difference in the comparison, the information of the test sample concentration can be calculated and obtained.
In the abovementioned optical inspection, all the possible error factors have to be controlled precisely, such as the error factors of the manufacturing processes of the illuminant, the photodiode and the band pass filter, or the error factors of the assembly of each part of the device. All these error factors may cause the inaccuracy of the measurement result.
In addition, the electrical signal produced by the photodiode is generated by the light irradiating to the PN junction of the photodiode. If the PN junction is not shaded by the test sample evenly, the electrical signal does not stand for the concentration of the test sample accurately.